This invention relates to the diagnosis and/or monitoring of patients with immunologic, hematologic, and inflammatory conditions and diseases. Measurement of complement ligand C4d and its receptor CR1 on surfaces of erythrocytes provides a highly sensitive and specific test for diagnosis and measurement of disease activity in patients with systemic lupus erythematosus (SLE) or scleroderma. See, e.g., PCT/US02/28910, which is herein incorporated by reference for all purposes. Patterns of complement ligand and receptor expression that facilitate diagnosis and disease activity monitoring in other human immunologic, hematologic, and inflammatory conditions and diseases have not been identified. The present invention addresses this and other needs.